I inquired the Steam forums about how to make units randomly wander an area. The response I got was from a well-known mod developer and he said that this can be accomplished by using "waypoint zones". I found nothing online or from my own experimenting in GEM Editor to suggest that this feature exists. The modder did not respond when I tried to contact him to clarify.

Note: I am aware of the "Zone" menu in GEM Editor, but I could not decipher
how to make a "waypoint zone"